Principles and embodiments of the present disclosure relate generally to curved glass production systems and methods.
Curved glass sheets are used in a variety of applications including automotive and architectural glass. For such applications, sheets of glass are precisely bent to defined shapes and/or curvatures determined by the configurations and sizes of the openings, as well as the vehicle style or architectural aesthetics. Such curved glass articles may be made by heating a flat glass sheet to a suitable temperature for forming, and applying forces to the sheet to change the shape.
Some glass bending methods involve heating the glass sheet in a lehr or furnace and forming the sheet while it is still in a high temperature state within the lehr or furnace. Glass sheets may also be bent by initially heating the glass sheet in a lehr or furnace to a suitable temperature, then transferring the glass sheet to a glass bending apparatus outside the lehr or furnace.
Glass sheets that undergo such bending operations have typically been 2.5 mm, 3 mm, or greater in thickness. Glass sheets with such thicknesses can have sufficient thermal mass that they do not cool down below suitable working temperatures, while being transferred from the furnace to the bending apparatus or during a bending operation.
Glass sheets with a thickness below about 2 mm, and in particular below about 1.6 mm typically do not have enough thermal mass to remain at a suitable working temperature, and become more challenging to bend because they tend to cool too quickly to bend in an acceptable manner.
The exit of a furnace is typically an opening in a furnace wall made of a refractory material such as firebrick or ceramic, which may or may not be covered by a moving door or restriction. Such constructions can introduce an unheated length into the glass sheet travel distance. In addition, there may be an unheated gap or transfer zone between the furnace exit and the entrance to a bending apparatus. These unheated regions provide a space where the glass sheet can lose heat and cool down.
In some instances, a glass sheet may be heated to a temperature higher than necessary for forming to offset such cooling effects. Heating the glass sheet to higher temperatures prior to bending, however, must be balanced between the benefit of having the part hot enough to bend, and the detriment of the higher temperature making the glass more susceptible to distortion and marking. Glass that is not at an appropriate temperature during a bending operation may exhibit optical distortions, such as roller waves (optical roll distortion) and/or discrete marking(s) and/or defect(s) that may make the bent sheet unsuitable for its intended purpose.
FIG. 1 illustrates a typical apparatus and process for bending glass sheets. Glass sheet 12 exits furnace 10, which includes a heat source comprised of a plurality of heating sections 14, only one of which is shown at the exit end of the furnace 10. The glass sheet is conveyed along a conveyor 16, which is shown as a plurality of rollers 18 supporting the glass sheet as is moves in the direction of arrow to a bender 22. Such a conveyor 16 including rollers is known as a roll conveyor. The bender 22 can be any suitable bending apparatus for producing bends in thin glass sheets to precisely form curved glass sheets. As shown in FIG. 1, there is a gap or space 30 between exit end 24 of the furnace and entrance end 26 of the bender 22. The exit end 24 of the furnace 10 is defined by an insulated wall, which is typically a refractory ceramic material.
An example of a commercial method of producing such curved glass sheets generally includes heating pre-trimmed, flat sheets of glass to the softening temperature in a furnace or lehr, press bending the heated sheets to a desired curvature between male and female mold members having complementary shaping surfaces, and cooling the curved sheets in a controlled manner. Such a bending technique is referred to as “press bending” and may suitably be carried out with the glass sheets oriented vertically, horizontally or obliquely. The glass sheets are typically conveyed to the press bender on a conveyor using a belt or rolls.
Another example of a commercial method of producing curved glass sheets in a roll bending station. For example, such a process would include heating pre-trimmed, flat sheets of glass to the softening temperature in a furnace or lehr, roll bending the heated sheets in a roll bender to a desired curvature, and cooling the curved sheets in a controlled manner. The glass sheets are typically conveyed from the furnace or lehr to the roll bender having horizontal rolls and laterally spaced sets of inclined rolls downstream from the furnace. The laterally spaced inclined rolls are typically provided in sets having progressively increasing inclination along the direction of conveyance to form each heated glass sheet during conveyance over or between sets of inclined rolls.
Generally, there has been a desire to produce thinner glass sheets for automotive glazing closures to provide closures that are lighter in weight and have lower production costs. Existing bending processes described above are capable of processing glass sheets thicker than 1.5 mm, they may not be suitable in the processing of glass sheets thinner than 1.6 mm, for example, thinner than 1 mm, or thinner than 0.8 mm. Furthermore, there is a challenge in providing quenching process that can quench glass sheets thinner than 2.6 mm. Accordingly, it would be desirable to provide apparatus and processes that a capable of quenching glass sheets thinner than 2.6 mm and/or producing curved glass sheets thinner than 1.6 mm in bending operations.